The ability to efficiently separate mixed materials, such as household recycling and construction waste, is of increasing importance and economic significance. For example, efficiently extracting and separating various types of recyclable materials from variable mixed waste streams is a critical factor when considering the economic viability of a recycling program. Material Recovery Facilities (MRFs) must be able to separate or sort mixed recyclable materials to a significantly high purity, for example 10 percent. If the final sorted and bailed product, for example similar plastic materials, does not achieve the purity required for purchase on the commodity market at a desired price, the product represents wasted resources and a financial loss for the MRF.
One step in the sorting or separation process is the dimensional sorting of materials. Dimensional separators employ various separation techniques to separate relatively light materials, for example, two-dimensional materials such as fibers, films; relatively heavier three-dimensional materials such as plastic, metal and certain large dimensional fibers; and materials of a relatively small dimension or fines, for example, crushed glass, shredded paper, and certain organic materials from one another. The small materials or fines are typically separated by providing voids or holes in a surface over which the various materials are separated. The fines pass through the surface and ultimately into a vessel or onto a conveyor belt for transfer.
It is relatively common that the fines resulting from such separation techniques contain a mixture of crushed glass and shredded paper. In order to achieve the desired purity of separated or classified material, it is necessary to further sort the resulting fine to separate the crushed glass from the shredded paper. Various techniques have been employed to achieve this stage of separation. For example, some Material Recovery Facilities (MRFs) employ a manual classification of the fines. Manual separation has the obvious shortcoming of being relatively inefficient and slow and relatively costly due to the need for increased employees.
Another type of fines classification employs trammel or drum separation techniques. Trammel classifiers use a generally horizontally oriented, hollow cylinder having corkscrew-like ribs or fins arranged on an interior surface. In operation, these classifiers separate fines by depositing the materials for separation into the interior of the cylinder and rotating the cylinder. The walls of the cylinder may have holes through which the smaller, heavier materials fall while the lighter materials such as fibers are carried or pushed by the rotating ribs to an opposite end of the cylinder. Trammel-type classifiers have the disadvantage of being relatively costly, occupying a relatively large amount of space in the MRF, and requiring relatively high maintenance due to the various rotating components and relatively high amount of dust and air born materials generated by the movement of the materials for separation within the cylinder.
Yet another technique for classifying fines employs optical recognition technology to identify certain types of fines materials and, upon identification, uses blowers, magnets or other removal means to extract the identified materials from the remainder of the fines. These classifiers have the disadvantage of being relatively costly, requiring relatively highly technically trained personnel to operate and maintain the complex optical hardware and software, and requiring relatively high maintenance costs of the components for extraction of the materials optically identified.
In view of the above described shortcomings of the known fines classifiers, there exists a significant need in the art for a fines classifier that employs a more efficient separation or classification technique requiring fewer moving components; a smaller footprint in the MRF, and decreased initial, maintenance, and repair costs.